(1) Field of the Invention
The invention relates to the fabrication of integrated circuit devices, and more particularly, to a new cold trap apparatus that is aimed at improving cold trap efficiency and improved operational characteristics.
(2) Description of the Prior Art
Trap devices are typically used together with vapor phase reaction apparatus. One of the most frequently applied processes that belongs to the vapor phase reaction class is the Chemical Vapor Deposition (CVD) process as part of which the gas that is used to perform the vapor deposition is removed from the deposition chamber and as such is included in the exhaust gas of the chamber. The level of gasses that are removed from the treatment chamber is, as part of a semiconductor manufacturing environment, controlled and captured by devices through which these gasses pass after being expulsed (by a vacuum pump) from the treatment chamber. The device that serves the function of capturing vacuum chamber treatment gasses is mostly connected between the chamber outlet and the vacuum pump that is used to pump residue gasses from the vacuum chamber. One of the reasons for removing residue gasses in this manner is to protect the vacuum pump from excessive wear that can be caused by the gasses that pass through it. The generic name for the devices that remove gasses from a gas stream is trap devices.
The principle that is most frequently used underlying the operation of the trap devices is cooling the gas that is to be cleaned and, in so doing, causing residue to accumulate inside the trap device from which these residues can readily be removed. The trap device therefore is typically equipped with a series of plates that are kept under temperature control and that intercept and react with the gasses that flow through the trap device and that come into contact with the series of plates. The plates are kept in a hermetically sealed container or vessel. The purpose of the plates within the trap device is to expose the gas that passes through the device to a particular temperature over as long a period of time as possible, the degree to which the trap device succeeds in doing this determines the cooling efficiency of the trap device. It is clear that it must be the objective of the design of any trap device to maximize the cooling efficiency of the device, this in combination with having a trap device that is not subject to undue damage as a result of its operation while the trap device must be cheap to operate and not be prone to frequent operational interruptions due to maintenance. In short: a trap device must be cheap to acquire and cheap to operate, have a high cooling efficiency, easy to clean and be sturdy enough that its operational lifetime is acceptable.
A number of trap devices increase their efficiency by not only keeping the plates that are mounted inside the trap as operational parts of the trap, but by further increasing the temperature difference between the gasses that impact the plates and the gasses. This is accomplished by heating the gasses before they impact the plates of the trap device. The heating trap can in effect already remove certain components from the exhaust gasses and can trap these components due to the fact that these components can adhere to the coils of the heating trap from where they can be removed. It is thereby again required that the heating surfaces over which the gasses pass must be maximized and that the process of heat exchange is optimized so that the maximum number and amount of components can be removed from the gasses. It is clear that the speed with which the gasses pass through heating and cooling gasses is of importance in determining the overall efficiency of the trap device.
It is further clear that trap devices can be designed for and aimed at treating exhaust gasses that are derived from particular processes since different processes will use different processing gasses for, for instance, the processes of various types of etching, vapor deposition and the like. These differences demonstrate themselves in different components that are contained in the exhaust gasses, in different concentrations of these components in the gasses and in different reactions of the exhaust gasses to sudden induced heating and cooling. It is therefore to be expected that a variety of trap devices are available, whereby each type of this variety is aimed at and best applied in a particular processing environment. To further complicate the application of trap devices, a number of chemical substances (for instance residual monomer vapor) can best be removed by passing the gasses through a filter that removes these components without the benefit of a rapid change in temperature of the gasses. This removal of a target component is, in most cases, not complete so that the gasses that have passed through the filter may need further treatment.
Of importance in the design of a trap device is also the design of the angle or angles under which the gas that passes through the device impacts the heating and/or cooling plates or coils. In many of the conventional designs, the heat exchanging sections are created in coil form, whereby the cooling or heating is provided by fluid that flows through the coils. This makes pumps, that are required to move the fluids through these coils, an integral part of the design of the trap device, this in addition to the type and heat exchange characteristics of the fluids that are used as the cooling or heating medium. As yet another design parameter for trap devices, the flow of the gasses that pass through the trap device can be controlled in either a passive (gravitational flow) or an active manner thereby providing yet another adjustment that can be used for improved efficiency of the trap device.